Ubiquitin E3 ligase MID1 inhibits the innate immune response by ubiquitinating IRF3

Midline 1 associated with Fas signaling enhances murine antigen-induced arthritis

Introduction

Rheumatoid arthritis is the most common immune-mediated joint disease, whose pathogenesis includes both innate and acquired immune mechanisms. Fas/Fas ligand system is considered to have a dual role in arthritis, inducing apoptotic cell death of hyperplastic synoviocytes and inflammatory cells, but also exerts proinflammatory effects. In our study, absence of Fas resulted in decreased accumulation of myeloid cells in affected joints.

Methods

Proportions of synovial hematopoietic cells were assessed by flow cytometry in wild-type and Fas -/- mice with antigen-induced arthritis. Effects of myeloid-specific ablation of Fas on the course of antigen-induced arthritis was assessed using Fasfl/LysMCre model. Arthritis was scored visually, histologically and by micro-computerized tomography. Transcriptome of sorted CD11b+Gr-1+ cells was analyzed by microarray, and effects of potential molecular driver Midline-1 (Mid-1) were analyzed in vitro and using Mid1 -/- mice.

Results

Ameliorated antigen-induced arthritis in Fas -/- mice is characterized by the lack of synovial accumulation of myeloid CD11b+Gr-1+ cells. However, myeloid-specific ablation of Fas was not sufficient to ameliorate arthritis, suggesting proinflammatory effects of Fas in multiple cell subsets in arthritis. Myeloid cells from Fas -/- mice downregulated limited number of genes including Mid1. Stimulation of bone marrow cells with low doses of soluble Fas agonist upregulated expression of Mid1. Inactivation of Mid1 had a variable anti-inflammatory effects in vitro and partial anti-arthritic effect in vivo.

Conclusion

Functional Fas is required for the recruitment and accumulation of innate inflammatory cells in arthritic joints. This accumulation is not driven exclusively by mediators expressed in accumulated subset. Mid1 enhances inflammatory polarization of myeloid cells and promotes bone and cartilage degradation in arthritis.

DNA-RNA hybrids in inflammation: sources, immune response, and therapeutic implications

Cytoplasmic DNA-RNA hybrids are emerging as important immunogenic nucleic acids, that were previously underappreciated. DNA-RNA hybrids, formed during cellular processes like transcription and replication, or by exogenous pathogens, are recognized by pattern recognition receptors (PRRs), including cGAS, DDX41, and TLR9, which trigger immune responses. Post-translational modifications (PTMs) including ubiquitination, phosphorylation, acetylation, and palmitoylation regulate the activity of PRRs and downstream signaling molecules, fine-tuning the immune response. Targeting enzymes involved in DNA-RNA hybrid metabolism and PTMs regulation offers therapeutic potential for inflammatory diseases. Herein, we discuss the sources, immune response, and therapeutic implications of DNA-RNA hybrids in inflammation, highlighting the significance of DNA-RNA hybrids as potential targets for the treatment of inflammation.

RNF149 modulates the type I IFN innate antiviral immune responses through degrading IRF3

E3 ubiquitin ligases are key molecules in regulating the innate immune responses against virus. They catalyze the activation or degradation of various signaling proteins involved in the innate immune responses. Herein, we found the regulatory role of RNF149 in the host's innate immune responses against viral infection. Virus infection induced the expression of RNF149. Overexpression of RNF149 was associated with reduced production of IFN-β and enhanced viral replication. Mechanically, RNF149 interacted with IRF3 and downregulated its protein level. As an E3 ubiquitin ligase, RNF149 promoted the K27-linked ubiquitination of IRF3 at K409 and K33-linked ubiquitination at K366 and K409, which promoted IRF3 degradation through the proteasome pathway. Our results revealed the regulatory mechanism of RNF149 during viral infection and provided new insights into host cells responding to viral infection. Downregulating the expression of RNF149 may help enhance the antiviral ability of host cells and inhibit viral replication, thus providing a new strategy for the treatment of viral infection.

USP5 inhibits anti-RNA viral innate immunity by deconjugating K48-linked unanchored and K63-linked anchored ubiquitin on IRF3

Interferon regulatory factor 3 (IRF3) is a central hub transcription factor that controls host antiviral innate immunity. The expression and function of IRF3 are tightly regulated by the post-translational modifications. However, it is unknown whether unanchored ubiquitination and deubiquitination of IRF3 involve modulating antiviral innate immunity against RNA viruses. Here, we find that USP5, a deubiquitinase (DUB) regulating unanchored polyubiquitin, is downregulated during host anti-RNA viral innate immunity in a type I interferon (IFN-I) receptor (IFNAR)-dependent manner. USP5 is further identified to inhibit IRF3-triggered antiviral immune responses through its DUB enzyme activity. K48-linked unanchored ubiquitin promotes IRF3-driven transcription of IFN-β and induction of IFN-stimulated genes (ISGs) in a dose-dependent manner. USP5 simultaneously removes both K48-linked unanchored and K63-linked anchored polyubiquitin chains on IRF3. Our study not only provides evidence that unanchored ubiquitin regulates anti-RNA viral innate immunity but also proposes a novel mechanism for DUB-controlled IRF3 activation, suggesting that USP5 is a potential target for the treatment of RNA viral infectious diseases.

Targeting TRAF6/IRF3 axis to inhibit NF-κB-p65 nuclear translocation enhances the chemosensitivity of 5-FU and reverses the proliferation of gastric cancer

Chemoresistance poses a significant clinical challenge in the treatment of gastric cancer (GC), while its underlying molecular mechanisms are still not fully understood. Post-translational protein modification and abnormal activation of nuclear factor-kappa B (NF-κB) are critical regulators of tumor chemoresistance. This study investigates the role of TNF receptors-associated factors 6 (TRAF6) in 5-Fluorouracil (5-FU) resistant GC. Utilizing short hairpin RNA (shRNA) to suppress TRAF6 expression in 5-FU resistant GC cells across both in vivo and in vitro models, we observed a marked reduction in cell proliferation and tumor growth. Low expression of TRAF6 inhibited nuclear translocation of NF-κB-p65, which was achieved by promoting the expression of Interferon regulatory factor 3 (IRF3). Importantly, TRAF6, an E3 ubiquitin ligase, bound to the IRF3-Δ (SR + IAD) (1-190aa) domain, inducing Lys70 ubiquitination of IRF3 to regulate its protein stability, with ubiquitin K48 residue playing a crucial role in this process. In conclusion, our study reveals the mechanism by which the TRAF6/IRF3 axis decreases GC's cells sensitivity to 5-FU by promoting nuclear translocation of NF-κB-p65, offering valuable insights into overcoming chemoresistance in GC.

The multiple roles of interferon regulatory factor family in health and disease

Interferon Regulatory Factors (IRFs), a family of transcription factors, profoundly influence the immune system, impacting both physiological and pathological processes. This review explores the diverse functions of nine mammalian IRF members, each featuring conserved domains essential for interactions with other transcription factors and cofactors. These interactions allow IRFs to modulate a broad spectrum of physiological processes, encompassing host defense, immune response, and cell development. Conversely, their pivotal role in immune regulation implicates them in the pathophysiology of various diseases, such as infectious diseases, autoimmune disorders, metabolic diseases, and cancers. In this context, IRFs display a dichotomous nature, functioning as both tumor suppressors and promoters, contingent upon the specific disease milieu. Post-translational modifications of IRFs, including phosphorylation and ubiquitination, play a crucial role in modulating their function, stability, and activation. As prospective biomarkers and therapeutic targets, IRFs present promising opportunities for disease intervention. Further research is needed to elucidate the precise mechanisms governing IRF regulation, potentially pioneering innovative therapeutic strategies, particularly in cancer treatment, where the equilibrium of IRF activities is of paramount importance.

Evolutionarily conserved Otub1 suppresses antiviral immune response by promoting Irf3 proteasomal degradation in miiuy croaker, Miichthys miiuy

Increasing evidence has been shown that OTUB1, a member of OTU deubiquitinases, is of importance in regulating the immune system. However, its molecular identification and functional characterization in teleosts are still rarely known. In this work, we cloned the otub1 of miiuy croaker (Miichthys miiuy), analyzed its sequence, structure, and evolution at genetic and protein levels, and determined its function in the antiviral immune response. The complete open reading frame (ORF) of miiuy croaker otub1 is 843 bp in length, encoding 280 amino acids. Miiuy croaker Otub1 has an OTU domain at the carboxyl terminus, which is a common functional domain that exists in OTU deubiquitinases. Molecular characteristics and evolution analysis results indicated that miiuy croaker Otub1, especially its functional domain, is highly conserved during evolution. The luciferase reporter assays showed that miiuy croaker Otub1 could significantly inhibit the poly(I:C) and Irf3-induced IFN1 and IFN-stimulated response element (ISRE) activation. Further experiments showed that miiuy croaker Otub1 decreases Irf3 protein abundance by promoting its proteasomal degradation. These data suggest that the evolutionarily conserved Otub1 acts as a suppressor in controlling antiviral immune response by promoting Irf3 proteasomal degradation in miiuy croaker.

TRIM Proteins and Antiviral Microtubule Reorganization: A Novel Component in Innate Immune Responses?

TRIM proteins are a family of innate immune factors that play diverse roles in innate immunity and protect the cell against viral and bacterial aggression. As part of this special issue on TRIM proteins, we will take advantage of our findings on TRIM69, which acts by reorganizing the microtubules (MTs) in a manner that is fundamentally antiviral, to more generally discuss how host-pathogen interactions that take place for the control of the MT network represent a crucial facet of the struggle that opposes viruses to their cell environment. In this context, we will present several other TRIM proteins that are known to interact with microtubules in situations other than viral infection, and we will discuss evidence that may suggest a possible contribution to viral control. Overall, the present review will highlight the importance that the control of the microtubule network bears in host-pathogen interactions.

Mid1 promotes synovitis in rheumatoid arthritis via ubiquitin-dependent post-translational modification

INTRODUCTION

Current anti-rheumatic drugs are primarily modulating immune cell activation, yet their effectiveness remained suboptimal. Therefore, novel therapeutics targeting alternative mechanisms, such as synovial activation, is urgently needed.

OBJECTIVES

To explore the role of Midline-1 (Mid1) in synovial activation.

METHODS

NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice were used to establish a subcutaneous xenograft model. Wild-type C57BL/6, Mid1-/-, Dpp4-/-, and Mid1-/-Dpp4-/- mice were used to establish a collagen-induced arthritis model. Cell viability, cell cycle, qPCR and western blotting analysis were used to detect MH7A proliferation, dipeptidyl peptidase-4 (DPP4) and Mid1 levels. Co-immunoprecipitation and proteomic analysis identified the candidate protein of Mid1 substrates. Ubiquitination assays were used to determine DPP4 ubiquitination status.

RESULTS

An increase in Mid1, an E3 ubiquitin ligase, was observed in human RA synovial tissue by GEO dataset analysis, and this elevation was confirmed in a collagen-induced mouse arthritis model. Notably, deletion of Mid1 in a collagen-induced arthritis model completely protected mice from developing arthritis. Subsequent overexpression and knockdown experiments on MH7A, a human synoviocyte cell line, unveiled a previously unrecognized role of Mid1 in synoviocyte proliferation and migration, the key aspects of synovial activation. Co-immunoprecipitation and proteomic analysis identified DPP4 as the most significant candidate of Mid1 substrates. Mechanistically, Mid1 promoted synoviocyte proliferation and migration by inducing ubiquitin-mediated proteasomal degradation of DPP4. DPP4 deficiency led to increased proliferation, migration, and inflammatory cytokine production in MH7A, while reconstitution of DPP4 significantly abolished Mid1-induced augmentation of cell proliferation and activation. Additionally, double knockout model showed that DPP4 deficiency abolished the protective effect of Mid1 defect on arthritis.

CONCLUSION

Overall, our findings suggest that the ubiquitination of DPP4 by Mid1 promotes synovial cell proliferation and invasion, exacerbating synovitis in RA. These results reveal a novel mechanism that controls synovial activation, positioning Mid1 as a promising target for therapeutic intervention in RA.

Deubiquitinase USP4 suppresses antitumor immunity by inhibiting IRF3 activation and tumor cell-intrinsic interferon response in colorectal cancer

Despite the approval of immune checkpoint blockade (ICB) therapy for various tumor types, its effectiveness is limited to only approximately 15% of patients with microsatellite instability-high (MSI-H) or mismatch repair deficiency (dMMR) colorectal cancer (CRC). Approximately 80%-85% of CRC patients have a microsatellite stability (MSS) phenotype, which features a rare T-cell infiltration. Thus, elucidating the mechanisms underlying resistance to ICB in patients with MSS CRC is imperative. In this study, we demonstrate that ubiquitin-specific peptidase 4 (USP4) is upregulated in MSS CRC tumors and negatively regulates the immune response against tumors in CRC. Additionally, USP4 represses the cellular interferon (IFN) response and antigen presentation and impairs PRR signaling-mediated cell death. Mechanistically, USP4 impedes the nuclear localization of interferon regulator Factor 3 (IRF3) by deubiquitinating the K63-polyubiquitin chain of TRAF6 and IRF3. Knockdown of USP4 enhances the infiltration of T cells in CRC tumors and overcomes ICB resistance in an MC38 syngeneic mouse model. Moreover, published datasets revealed that patients showing higher USP4 expression exhibited decreased responsiveness to anti-PD-L1 therapy. These findings highlight an essential role of USP4 in the suppression of antitumor immunity in CRC.

Midline-1 regulates effector T cell motility in experimental autoimmune encephalomyelitis via mTOR/microtubule pathway

Background: Effector T cell activation, migration, and proinflammatory cytokine production are crucial steps in autoimmune disorders such as multiple sclerosis (MS). While several therapeutic approaches targeting T cell activation and proinflammatory cytokines have been developed for the treatment of autoimmune diseases, there are no therapeutic agents targeting the migration of effector T cells, largely due to our limited understanding of regulatory mechanisms of T cell migration in autoimmune disease. Here we reported that midline-1 (Mid1) is a key regulator of effector T cell migration in experimental autoimmune encephalomyelitis (EAE), a widely used animal model of MS. Methods: Mid1-/- mice were generated by Crispr-Cas9 technology. T cell-specific Mid1 knockout chimeric mice were generated by adoptive transfer of Mid1-/- T cells into lymphocyte deficient Rag2-/- mice. Mice were either immunized with MOG35-55 (active EAE) or received adoptive transfer of pathogenic T cells (passive EAE) to induce EAE. In vitro Transwell® assay or in vivo footpad injection were used to assess the migration of T cells. Results: Mid1 was significantly increased in the spinal cord of wild-type (Wt) EAE mice and disruption of Mid1 in T cells markedly suppressed the development of both active and passive EAE. Transcriptomic and flow cytometric analyses revealed a marked reduction in effector T cell number in the central nervous system of Mid1-/- mice after EAE induction. Conversely, an increase in the number of T cells was observed in the draining lymph nodes of Mid1-/- mice. Mice that were adoptively transferred with pathogenic Mid1-/- T cells also exhibited milder symptoms of EAE, along with a lower T cell count in the spinal cord. Additionally, disruption of Mid1 significantly inhibited T-cell migration both in vivo and in vitro. RNA sequencing suggests a suppression in multiple inflammatory pathways in Mid1-/- mice, including mTOR signaling that plays a critical role in cell migration. Subsequent experiments confirmed the interaction between Mid1 and mTOR. Suppression of mTOR with rapamycin or microtubule spindle formation with colcemid blunted the regulatory effect of Mid1 on T cell migration. In addition, mTOR agonists MHY1485 and 3BDO restored the migratory deficit caused by Mid1 depletion. Conclusion: Our data suggests that Mid1 regulates effector T cell migration to the central nervous system via mTOR/microtubule pathway in EAE, and thus may serve as a potential therapeutic target for the treatment of MS.

Human OTUD6B positively regulates type I IFN antiviral innate immune responses by deubiquitinating and stabilizing IRF3

IMPORTANCE

Interferon (IFN) regulatory factor (IRF3) is one of the key factors for type I IFN transcription. To sophisticatedly regulate type I IFN antiviral immune response, IRF3 activity is closely controlled by a variety of post-translational modifications. However, the regulatory mechanisms are still not fully elucidated. In the present study, we found that human deubiquitinase OTUD6B positively regulates IRF3-mediated antiviral immune response. OTUD6B can stabilize the IRF3 protein level via hydrolyzing (Lys33)-linked polyubiquitin at Lys315. More importantly, mice with OTUD6B overexpression exhibited more resistance to RNA virus infection. Thus, unlike the previous report that zebrafish OTUD6B negatively regulates the antiviral response by suppressing K63-linked ubiquitination of IRF3 and IRF7, we demonstrate that human OTUD6B actually enhances type I IFN response and has the potential for antiviral therapy.

A Golgi-resident GPR108 cooperates with E3 ubiquitin ligase Smurf1 to suppress antiviral innate immunity

The regulation of antiviral immunity is crucial in maintaining host immune homeostasis, a process that involves dynamic modulations of host organelles. The Golgi apparatus is increasingly perceived as a host organelle functioning as a critical platform for innate immunity, but the detailed mechanism by which it regulates antiviral immunity remains elusive. Here, we identify the Golgi-localized G protein-coupled receptor 108 (GPR108) as a regulator of type Ι interferon responses by targeting interferon regulatory factor 3 (IRF3). Mechanistically, GPR108 enhances the ubiquitin ligase Smad ubiquitylation regulatory factor 1 (Smurf1)-mediated K63-linked polyubiquitination of phosphorylated IRF3 for nuclear dot 10 protein 52 (NDP52)-dependent autophagic degradation, leading to suppression of antiviral immune responses against DNA or RNA viruses. Taken together, our study provides insight into the crosstalk between the Golgi apparatus and antiviral immunity via a dynamic and spatiotemporal regulation of GPR108-Smurf1 axis, thereby indicating a potential target for treating viral infection.

E3 Ubiquitin Ligases: The Operators of the Ubiquitin Code That Regulates the RLR and cGAS-STING Pathways

The outbreaks caused by RNA and DNA viruses, such as SARS-CoV-2 and monkeypox, pose serious threats to human health. The RLR and cGAS-STING pathways contain major cytoplasmic sensors and signaling transduction axes for host innate antiviral immunity. In physiological and virus-induced pathological states, the activation and inactivation of these signal axes are tightly controlled, especially post-translational modifications (PTMs). E3 ubiquitin ligases (E3s) are the direct manipulator of ubiquitin codons and determine the type and modification type of substrate proteins. Therefore, members of the E3s family are involved in balancing the host's innate antiviral immune responses, and their functions have been extensively studied over recent decades. In this study, we overviewed the mechanisms of different members of three E3s families that mediate the RLR and cGAS-STING axes and analyzed them as potential molecular targets for the prevention and treatment of virus-related diseases.

The Capsid Protein of Nervous Necrosis Virus Antagonizes Host Type I IFN Production by a Dual Strategy to Negatively Regulate Retinoic Acid-Inducible Gene-I-like Receptor Pathways

Nervous necrosis virus (NNV), a highly pathogenic RNA virus, is a major pathogen in the global aquaculture industry. To efficiently infect fish, NNV must evade or subvert the host IFN for their replication; however, the precise mechanisms remain to be elucidated. In this study, we reported that capsid protein (CP) of red-spotted grouper NNV (RGNNV) suppressed the IFN antiviral response to promote RGNNV replication in Lateolabrax japonicus brain cells, which depended on the ARM, S, and P domains of CP. CP showed an indirect or direct association with the key components of retinoic acid-inducible gene-I-like receptors signaling, L. japonicus TNFR-associated factor 3 (LjTRAF3) and IFN regulatory factor (LjIRF3), respectively, and degraded LjTRAF3 and LjIRF3 through the ubiquitin-proteasome pathway in HEK293T cells. Furthermore, we found that CP potentiated LjTRAF3 K48 ubiquitination degradation in a L. japonicus ring finger protein 114-dependent manner. LjIRF3 interacted with CP through the S domain of CP and the transcriptional activation domain or regulatory domain of LjIRF3. CP promoted LjIRF3 K48 ubiquitination degradation, leading to the reduced phosphorylation level and nuclear translocation of LjIRF3. Taken together, we demonstrated that CP inhibited type I IFN response by a dual strategy to potentiate the ubiquitination degradation of LjTRAF3 and LjIRF3. This study reveals a novel mechanism of RGNNV evading host immune response via its CP protein that will provide insights into the complex pathogenesis of NNV.

E3 ubiquitin ligase MID1 ubiquitinates and degrades type-I interferon receptor 2

Type I interferon (IFN-I) is a common biological molecule used for the treatment of viral diseases. However, the clinical antiviral efficacy of IFN-I needs to be greatly improved. In this study, IFN-I receptor 2 (IFNAR2) was revealed to undergo degradation at the protein level in cells treated with IFN-I for long periods of time. Further studies found a physical interaction between the E3 ubiquitin ligase Midline-1 (MID1) and IFNAR2. As a consequence, MID1 induced both K48-linked and K63-linked polyubiquitination of IFNAR2, which promoted IFNAR2 protein degradation in a lysosome-dependent manner. Conversely, knockdown of MID1 largely restricted IFN-I-induced degradation of IFNAR2. Importantly, MID1 regulated the strength of IFN-I signaling and IFN-I-induced antiviral activity. These findings reveal a regulatory mechanism of IFNAR2 ubiquitination and protein stability in IFN-I signaling, which could provide a potential target for improving the antiviral efficacy of IFN-I.

The Role of Long Noncoding RNA BST2-2 in the Innate Immune Response to Viral Infection

Long noncoding RNAs (lncRNAs) widely exist in the cells and play important roles in various biological processes. The role of lncRNAs in immunity remains largely unknown. lncRNA BST2-2 (lncBST2-2) was upregulated upon viral infection and dependent on the interferon (IFN)/JAK/STAT signaling pathway. There was no coding potential found in the lncBST2-2 transcript. Overexpression of lncBST2-2 inhibited the replication of hepatitis C virus (HCV), Newcastle disease virus (NDV), vesicular stomatitis virus (VSV), and herpes simplex virus (HSV), while knockdown of lncBST2-2 facilitated viral replication. Further studies showed that lncBST2-2 promoted the phosphorylation, dimerization, and nuclear transport of IRF3, promoting the production of IFNs. Importantly, lncBST2-2 interacted with the DNA-binding domain of IRF3, which augmented TBK1 and IRF3 interaction, thereby inducing robust production of IFNs. Moreover, lncBST2-2 impaired the interaction between IRF3 and PP2A-RACK1 complex, an essential step for the dephosphorylation of IRF3. These data shown that lncBST2-2 promotes the innate immune response to viral infection through targeting IRF3. Our study reveals the lncRNA involved in the activation of IRF3 and provides a new insight into the role of lncRNA in antiviral innate immunity. IMPORTANCE Innate immunity is an important part of the human immune system to resist the invasion of foreign pathogens. IRF3 plays a critical role in the innate immune response to viral infection. In this study, we demonstrated that lncBST2-2 plays an important role in innate immunity. Virus-induced lncBST2-2 positively regulates innate immunity by interacting with IRF3 and blocking the dephosphorylation effect of RACK1-PP2A complex on IRF3, thus inhibiting viral infection. Our study provides a new insight into the role of lncBST2-2 in the regulation of IRF3 signaling activation.

Ubiquitylation of cyclin C by HACE1 regulates cisplatin-associated sensitivity in gastric cancer

BACKGROUND

Cyclin C (CCNC) was reported to take part in regulating mitochondria-derived oxidative stress under cisplatin stimulation. However, its effect in gastric cancer is unknown. This study aimed to investigate the role of cyclin C and its ubiquitylation in regulating cisplatin resistance in gastric cancer.

METHODS

The interaction between HECT domain and ankyrin repeat-containing E3 ubiquitin-protein ligase 1 (HACE1) and cyclin C was investigated by GST pull-down assay, co-immunoprecipitation and ubiquitylation assay. Mitochondria-derived oxidative stress was studied by MitoSOX Red assay, seahorse assay and mitochondrial membrane potential measurement. Cyclin C-associated cisplatin resistance was studied in vivo via xenograft.

RESULTS

HACE1 catalysed the ubiquitylation of cyclin C by adding Lys11-linked ubiquitin chains when cyclin C translocates to cytoplasm induced by cisplatin treatment. The ubiquitin-modified cyclin C then anchor at mitochondira, which induced mitochondrial fission and ROS synthesis. Depleting CCNC or mutation on the ubiquitylation sites decreased mitochondrial ROS production and reduced cell apoptosis under cisplatin treatment. Xenograft study showed that disrupting cyclin C ubiquitylation by HACE1 conferred impairing cell apoptosis response upon cisplatin administration.

CONCLUSIONS

Cyclin C is a newly identified substrate of HACE1 E3 ligase. HACE1-mediated ubiquitylation of cyclin C sheds light on a better understanding of cisplatin-associated resistance in gastric cancer patients. Ubiquitylation of cyclin C by HACE1 regulates cisplatin-associated sensitivity in gastric cancer. With cisplatin-induced nuclear-mitochondrial translocation of cyclin C, its ubiquitylation by HACE1 increased mitochondrial fission and mitochondrial-derived oxidative stress, leading to cell apoptosis.

SARS-CoV-2 Spike Antagonizes Innate Antiviral Immunity by Targeting Interferon Regulatory Factor 3

Corona virus disease 2019 (COVID-19) pathogenesis is intimately linked to the severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) and disease severity has been associated with compromised induction of type I interferon (IFN-I) cytokines which coordinate the innate immune response to virus infections. Here we identified the SARS-CoV-2 encoded protein, Spike, as an inhibitor of IFN-I that antagonizes viral RNA pattern recognition receptor RIG-I signaling. Ectopic expression of SARS-CoV-2 Spike blocked RIG-I mediated activation of IFNβ and downstream induction of interferon stimulated genes. Consequently, SARS-CoV-2 Spike expressing cells harbored increased RNA viral burden compared to control cells. Co-immunoprecipitation experiments revealed SARS-CoV-2 Spike associated with interferon regulatory factor 3 (IRF3), a key transcription factor that governs IFN-I activation. Co-expression analysis via immunoassays further indicated Spike specifically suppressed IRF3 expression as NF-κB and STAT1 transcription factor levels remained intact. Further biochemical experiments uncovered SARS-CoV-2 Spike potentiated proteasomal degradation of IRF3, implicating a novel mechanism by which SARS-CoV-2 evades the host innate antiviral immune response to facilitate COVID-19 pathogenesis.

Neurodevelopmental Disorders (NDD) Caused by Genomic Alterations of the Ubiquitin-Proteasome System (UPS): the Possible Contribution of Immune Dysregulation to Disease Pathogenesis

Over thirty years have passed since the first description of ubiquitin-positive structures in the brain of patients suffering from Alzheimer’s disease. Meanwhile, the intracellular accumulation of ubiquitin-modified insoluble protein aggregates has become an indisputable hallmark of neurodegeneration. However, the role of ubiquitin and a fortiori the ubiquitin-proteasome system (UPS) in the pathogenesis of neurodevelopmental disorders (NDD) is much less described. In this article, we review all reported monogenic forms of NDD caused by lesions in genes coding for any component of the UPS including ubiquitin-activating (E1), -conjugating (E2) enzymes, ubiquitin ligases (E3), ubiquitin hydrolases, and ubiquitin-like modifiers as well as proteasome subunits. Strikingly, our analysis revealed that a vast majority of these proteins have a described function in the negative regulation of the innate immune response. In this work, we hypothesize a possible involvement of autoinflammation in NDD pathogenesis. Herein, we discuss the parallels between immune dysregulation and neurodevelopment with the aim at improving our understanding the biology of NDD and providing knowledge required for the design of novel therapeutic strategies.

TRIM18-Regulated STAT3 Signaling Pathway via PTP1B Promotes Renal Epithelial-Mesenchymal Transition, Inflammation, and Fibrosis in Diabetic Kidney Disease

Diabetic kidney disease (DKD) has become a key cause of end-stage renal disease worldwide. Inflammation and fibrosis have been shown to play important roles in the pathogenesis of DKD. MID1, also known as TRIM18, is an E3 ubiquitin ligase of the tripartite motif (TRIM) subfamily of RING-containing proteins and increased in renal tubule in patients with DKD. However, the function and molecular mechanism of TRIM18 in DKD remain unexplored. Herein we report that TRIM18 expression levels were increased in patients with DKD. An animal study confirms that TRIM18 is involved in kidney injury and fibrosis in diabetic mice. TRIM18 knockdown inhibits high glucose (HG)-induced epithelial–mesenchymal transition (EMT), inflammation, and fibrosis of HK-2 cells. This is accompanied by decreased levels of tumor necrosis factor alpha, interleukin-6, hydroxyproline (Hyp), connective tissue growth factor, and α-smooth muscle actin. Additionally, TRIM18 knockdown inhibits HG-induced increase in the phosphorylated-/total signal transducer and activator of transcription (STAT3). Treatment with niclosamide (STAT3 inhibitor) or protein tyrosine phosphatase-1B (PTP1B) overexpression blocked the TRIM18 induced EMT, inflammation and fibrosis. Co-immunoprecipitation and Western blot assays showed that TRIM18 promoted the ubiquitination of PTP1B. These findings highlight the importance of the TRIM18/PTP1B/STAT3 signaling pathway in DKD and can help in the development of new therapeutics for DKD treatment.

BTK Promotes Atherosclerosis by Regulating Oxidative Stress, Mitochondrial Injury, and ER Stress of Macrophages

Atherosclerosis (AS) is a chronic metabolic disease in arterial walls, characterized by lipid deposition and persistent aseptic inflammation. AS is regarded as the basis of a variety of cardiovascular and cerebrovascular diseases. It is widely acknowledged that macrophages would become foam cells after internalizing lipoprotein particles, which is an initial factor in atherogenesis. Here, we showed the influences of Bruton's tyrosine kinase (BTK) in macrophage-mediated AS and how BTK regulates the inflammatory responses of macrophages in AS. Our bioinformatic results suggested that BTK was a potential hub gene, which is closely related to oxidative stress, ER stress, and inflammation in macrophage-induced AS. Moreover, we found that BTK knockdown could restrain ox-LDL-induced NK-κB signaling activation in macrophages and repressed M1 polarization. The mechanistic studies revealed that oxidative stress, mitochondrial injury, and ER stress in macrophages were also suppressed by BTK knockdown. Furthermore, we found that sh-BTK adenovirus injection could alleviate the severity of AS in ApoE-/- mice induced by a high-fat diet in vivo. Our study suggested that BTK promoted ox-LDL-induced ER stress, oxidative stress, and inflammatory responses in macrophages, and it may be a potential therapeutic target in AS.